Comparison of strength envelopes of RC columns with shear strength models

Abstract

The experimental strengths of twelve reinforced concrete columns, tested under the effect of constant axial load and cyclic lateral load, and the shear capacities obtained from seven widely accepted shear strength models were evaluated in this study. The shear spans, stirrup diameters, concrete strength, and axial load indexes of the columns were considered as parameters. Three of the shear strength models evaluated were regulation/code models. The other five models were shear strength envelope models that consider the shear strength degradation depending on cyclic loading and increasing ductility demand. The evaluation result showed that models of shear strength envelope are quite successful in both determining strength and simulating shear strength degradation. Regulation models take a conservative approach to design, but it has been observed that strength degradation with cyclic loading should be considered. Columns with a shear span of 1.5 are critical to shear-dominant behavior and regulations should take this into account. A further consideration is required for all models in assessing the effect of axial load index on behavior under cyclic loading.

Keywords

• RC columns
• cyclic load
• shear strength
• strength degradation models

Betonarme kolonların dayanım zarflarının kesme dayanımı modelleri ile karşılaştırılması

Öz

Bu çalışmada sabit eksenel yük ve çevrimsel yatay yük etkisi altında test edilen oniki adet betonarme kolonun deneysel dayanımları ile yaygın olarak kabul gören yedi kesme dayanımı modelinden elde edilen kesme kapasiteleri değerlendirilmiştir. Bu değerlendirmede kolonların kesme açıklığı oranları, etriye çapları, beton dayanımları ve eksenel yük indeksleri birer parametre olarak dikkate alınmıştır. Değerlendirmeye alınan kesme dayanımı modellerinden üçü yönetmelik modelleridir. Diğer dört model ise artan düktilite talebine bağlı olarak çevrimsel yükleme ile kesme dayanımı azalmasını dikkate alan kesme dayanımı zarfı modelleridir. Değerlendirme neticesinde kesme dayanımı zarfları hem dayanımın belirlenmesinde hem de kesme dayanımı azalmasının benzeşiminde oldukça başarılı olmuştur. Yönetmelik modellerinin tasarıma yönelik olarak ihtiyatlı sonuçlar verdiği, ancak çevrimsel yükleme ile dayanım azalmasının dikkate alınması gerektiği görülmüştür. Kesme açıklığı oranı 1.5 olan kolonlar kesme hakim davranış için kritiktir ve yönetmeliklerde bu durum dikkate alınmalıdır. Eksenel yük indeksinin çevrimsel yük etkisi altında davranışa etkisi tüm modeller tarafından ayrıca ele alınmalıdır.

Anahtar Kelimeler

• Betonarme kolon
• çevrimsel yük
• kesme dayanımı
• dayanım azalması modelleri

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